Question was posted 6 months ago, but not yet answered, so thought I'd give it a try as my first post

According to the "Exchange rate" section of A-Club T&C:

http://www.a-club.com/en/terms-and-c...s.html#anchor7

"The applied exchange rate is that of the last work-day of the month preceding the stay for which the transaction was recorded. This rate is extracted from the multi-currency “Multidevises” database for currency and financial information at Natixis bank"

The "Multidevises" database is available on the web at https://www.multidevises.com/Accueil.jsp?lang=en, so you can theoretically double-check the rates applied. But you have to pay a subscription to access this service... Paying to see exchange rate data online nowadays?